Red-emitting phosphors based on complex fluoride materials activated by Mn4+, such as those described in U.S. Pat. Nos. 7,358,542, 7,497,973, and 7,648,649, can be utilized in combination with yellow/green emitting phosphors such as YAG:Ce or other garnet compositions to achieve warm white light (CCTs<5000 K on the blackbody locus, color rendering index (CRI>80)) from a blue LED, equivalent to that produced by current fluorescent, incandescent and halogen lamps. These materials absorb blue light strongly and efficiently emit between about 610-635 nanometers (nm) with little deep red/NIR emission. Therefore, luminous efficacy is maximized compared to other red phosphors that have significant emission in the deeper red where eye sensitivity is poor. Quantum efficiency can exceed to 85% under blue (440-460 nm) excitation.
While the efficacy and CRI of lighting systems using Mn4+ activated (or doped) complex fluoride materials can be quite high, one potential limitation is material's susceptibility to degradation under fabrication and use conditions, for example high temperature and humidity (HTHH) conditions. It may be possible to reduce the degradation of the material using post-synthesis processing steps, as described in U.S. Pat. No. 8,252,613. However, development of improved methods for reducing or preventing degradation of the materials is desirable.